As China dismantles its planned economy, more than a 100 million migrant workers have left their homes in the countryside to find jobs in cities. Most of those working in labor-intensive industries are women, who endure long hours with no rest, and sometimes no pay.

Zhang Xiaoyu did not think twice about handing her life savings over to the boss when she started her restaurant job.

But after three months of working 13-hour days, seven days a week, Ms. Zhang complains she has only received a fraction of the wage she was promised.

The 21-year-old traveled 600 kilometers from her village in Shanxi province, central China, to work in Beijing. She borrowed money from friends to fund her trip, and hoped to send money home each month to support her parents and two sisters.

Ms. Zhang says she accepted a job cleaning and serving food at the Sunshine hotel-restaurant because her boss promised her Sundays off. She paid a deposit of $24, half her expected monthly wage. In exchange, she was given room and board in the basement, along with 16 other mostly women workers.

Yet Ms. Zhang was never allowed to rest on Sunday, because her boss said there was too much to do. Then came the fines. She says she accidentally broke two glasses, and was charged $6. Another time, Ms. Zhang says she went up to the roof for some air, and was fined for not working enough.

She wants to quit, but the boss refuses to return her deposit, and still owes her almost two months' wages. "All the workers are unhappy," she said, "but no one dares leave because they are afraid they cannot find a job anywhere else."

Ms. Zhang's story illustrates a growing trend in China of what some scholars call bonded labor. As China's supply of cheap, migrant labor rises, employers are finding more and more ways to exploit their workers.

Migrant women are especially vulnerable to labor abuses and discrimination. Women comprise most of the workforce in low-wage, unskilled and labor-intensive industries.

A survey by China's women's federation last year showed that urban women make around two-thirds of what men earn for the same work. In the countryside, women make less than half of a man's wage.

To make matters worse, southern cities such as Guangzhou and Shenzhen - the most popular destinations for low-skilled, migrant women - are cracking down on temporary workers.

All workers must now obtain residency permits through their employers, who in turn must prove that they follow the government's hiring rules. The new policy requires companies to hire about half of their staff from the city's permanent residents. Migrants without the right documents will be detained and sent back home.

But labor experts say such crackdowns only create a greater climate of fear among migrant workers, making them more vulnerable to abuse.

Anita Chan, a Chinese labor specialist at the Australian National University, says employers increasingly withhold wages, confident that their laborers will not find work elsewhere. "Owing workers wages for two or three months or even more is quite common," she said. "The workers are not sure when they can get their wages, so they just keep on working. Then the more they work, the more wages they're being owed."

Ms. Chan says some enterprises demand a hefty deposit before the employee starts a new job. Others take away the migrant's temporary residence permit, preventing her from seeking work at another company.

China's labor law of 1995 forbids employers from withholding wages or collecting deposits. The law also mandates a 40-hour work week, a minimum wage, and grants women workers maternity leave. But these laws are rarely enforced.

Ms. Chan says abuses are the worst in smaller enterprises, where employers often use force to maintain worker discipline. "It is very common in Chinese factories to have security guards at the door to keep track of things, so people can't walk in and out, and also to check on workers," said Anita Chan. "Also sometimes they are connected with the police. So there is a lot of violence, because these people have no power. There is no respect for them; there is no dignity."

In Beijing, the worker Zhang Xiaoyu has decided to fight for her dignity. She is quitting her job and seeking legal help to win back her deposit and unpaid wages.

"My employer claims she cannot afford to pay the workers," said Ms. Zhang. "But if that is true, why does the boss have a nice house, a car and a cell phone," she complains.

"People like me left our families and came from hundreds or thousands of kilometers away to work," she said. "Maybe we are not dying of starvation, but we came here to make money, and we cannot even save a penny."